This helps to Minimize Mutable State - Mutable state makes mistakes more likely. If you don’t need to change a variable, it’s probably a good idea to use const. on the window object) if defined outside a block. Constants can be declared with uppercase or lowercase letters - a common convention is to use all-uppercase letters.Ī constant can have global scope (i.e. If you define an object using const, the object contents can be amended.Ī constant can’t have the same name as a function or variable in the same scope. However, the value held by a constant is not immutable. You can’t change the value of a constant by re-assignment, and it can’t be re-declared. Variables declared in this way are read-only constants. This is another way to declare variables - like let, variables const has block scope. Variables defined with var and const are function scoped, whereas variables defined with let are block-scoped.īlock scoping basically means that the variable scope is limited by the enclosing )) // returns Array const: Declare a block-scoped read-only constant.

let: Declare a block-scoped local variable, optionally assigning a value.var: Declare a variable, optionally assigning a value.This means that variables can be declared as follows: Variable DeclarationĮcmascript 6 introduced the let and const statements for declaring variables. Use a transpiler like babel to sort things out for pre-ES6 browsers. TLDR ĭon’t use var to declare variables - use const where possible and let otherwise. In JavaScript, identifiers are case-sensitive and must begin with a letter, underscore or dollar sign. Variable names are known as ‘identifiers’. It’s the next version of JavaScript, and it has some great new features.

Next up: getting familiar with a few important JavaScript array methods and scripting a voice-sensitive robot animation! Also, find out about a great front-end framework called Vue.Variables are used as symbolic names for values. You’ve probably heard about ECMAScript 6 (or ES6) already. class CircleĪnd that was a short introduction to some of the features of JavaScript ES6. That means this does not add a new object model or anything fancy like that. While it is merely syntactic sugar over the already available protytype-based classes, it does serve to enhance code clarity. Formal Class Definition Syntax Class DefinitionĪnd finally, JavaScript gets a formal class definition syntax.

Ecma 6